The objective of the proposed research is to elucidate mechanisms of single cellular and multicellular morphogenesis. The early development of neurons will be analyzed under simplified environmental conditions, using procedures that will permit detailed study of: the transition from precursor cell to neuron; axon initiation; and motility characteristics of neuronal surfaces. The degree to which neurite branching patterns and morphology are intrinsic properties of a given neuronal type, as opposed to being environmentally imposed, will be investigated. The ultrastructure of neuronal cell cortices will be examined in regions of continuing motility and at sties where motility is arrested. Contact inhibition of growth cones and glial cells will be compared and related to cytoskeletal morphology. Morphogenesis of embryonic mammalian salivary gland and lung epithelia will be studied, using high resolution time-lapse cinematography. In particular, the highly dynamic epithelial surface will be studied with respect to the initial event of branching morphogenesis. The epithelial surface will be marked so that tissue and cell movements may be followed as branching occurs. Ultrastructural analysis of such sites, using both transmission and scanning electron microscopy, will be performed, and drug treatments will be used to investigate possible roles of microtubules and microfilaments during the first step of morphogenesis.